Apparatus for burning carbonaceous material in a fluidized bed reactor

ABSTRACT

A method and apparatus for burning carbonaceous materials in a fluidized bed reactor comprising a bottom region and a top region, and containing a fluidized bed, with the heat of combustion being dissipated at least via wall cooling surfaces, and comprising a recirculation system, including a labyrinth separator for recirculating the separated solids to the bottom region of the fluidized bed reactor. The solids are separated from the rising flow of flue gas by the labyrinth separator, which is disposed directly in the top region of the fluidized bed reactor, and are conveyed in the reactor itself along the wall cooling surfaces and are supplied to the bottom region of the reactor, either freely or in closed or partly or completely open recirculation passages. The main area of application is with a steam generator.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for burningcarbonaceous material in a fluidized bed reactor that includes: a bottomportion; a top portion; wall cooling surfaces; a recirculation or returnsystem that includes at least one labyrinth separator which serves forthe return of separated-off solid material to the bottom portion and isprovided with staggered beams that have an essentially U-shapedcross-sectional configuration and are open toward a rising flow of fluegas; a fuel supply, a fluidizing air supply, and a secondary air supplyin the bottom portion; and at least one dust separator disposeddownstream of the at least one labyrinth separator.

WO 83/03294 discloses a boiler having a circulating fluidized bed; thefuel is introduced into a fluidized bed reactor which is free of bafflesand has wall cooling surfaces. The flue gas, which is charged withsolids, is deflected through 90° and leaves the fluidized bed reactor atthe top end thereof and flows along a horizontal flue-gas line to adescending flue. The gas is then again deflected substantially through90° and enters a rising flue in which convective heating surfaces aredisposed.

A non-centrifugal mechanical separator in the form of a labyrinthseparator is disposed in the connecting line and in the descending flue.The separator elements in the connecting line extend substantiallyvertically, and the solid material separated by them is conveyed to astorage chamber disposed between the fluidized bed reactor and thedescending flue. The separator elements in the descending flue slopedown towards the storage chamber, so that the solids separated by themcan likewise be supplied thereto. The bottom end of the storage chamberis connected by a number of "L-valves" to the bottom portion of thefluidized bed reactor, so that the solids deposited in the storagechamber can be recirculated in a controlled manner, by means of afluidizing device associated with the L-valve, to the bottom region ofthe reactor above the valve tray therein. In WO 83/03294, as in thepresent specification and claims, the term "labyrinth separator" means aseparator where separation occurs through gravity and/or momentum, i.e.without centrifugal force. In the known boiler, staggered lines orchutes are used that extend substantially transverse to the flow of fluegas and that open toward it in a substantially U-shape.

The disadvantage of the known boiler is that the storage chamber, whichis disposed outside the reactor, together with one or more L-valvesconnected downstream, are necessary for the recirculation system, whichis external; i.e. separate ash lines and corresponding conveying andregulating equipment are needed.

It is therefore an object of the present invention to provide a methodwhere it is no longer necessary to remove the solids from the fluidizedbed reactor.

SUMMARY OF THE INVENTION

To this end, according to the invention, the labyrinth separator, whichis disposed directly in the top region of the fluidized bed reactor,separates the solids from the rising flow of flue gas and supplies themin the fluidized bed reactor itself, along the wall cooling surfaces, tothe bottom region of the reactor.

The result is to simplify the recirculation or return of solids to thefurnace or firing unit.

The separated solids can advantageously be recirculated along theexposed wall cooling surfaces without further protection against therising flue gases, or alternatively the separated solids can berecirculated via recirculation lines or passages formed in the reactor;the passages can be closed-off by a wall from the reactor interior, orpreferably can be partly or completely open, leaving only web-like sidewalls in the latter case. The partial opening can be in the form of alongitudinally slotted outer wall or an outer wall that is provided withapertures disposed in lines.

Advantageously also, the recirculation passages terminate in the bottomregion in the area of operation of the secondary air supply, so that theintroduced solids are thoroughly mixed with the other fluidized bedmaterial and the temperature is correspondingly equalized, since thesolids recirculated along the wall have been appropriately cooled.

In the boiler according to WO 83/03294 the labyrinth separator elementsare not cooled and consequently, for reasons of thermal expansion,cannot be permanently connected at one end to the wall of the fluidizedbed reactor. By contrast, according to an advantageous feature of thepresent invention the labyrinth separator is cooled.

The invention also relates to an apparatus for burning carbonaceousmaterials in a fluidized bed reactor comprising a bottom region and atop region, at least with wall cooling surfaces and with a recirculationsystem including at least one labyrinth separator for recirculatingseparated solids to the bottom region of the reactor, with a fuelsupply, a supply of fluidizing air and a preferably stepped secondaryair supply in the bottom region, and at least one dust separator, e.g. amulticyclone or fibrous filter, that is connected behind or downstreamof the labyrinth separator.

Advantageously, in the device according to the invention the labyrinthseparator is disposed directly in the top region of the fluidized bedreactor and conveys the separated solids to at least one wall coolingsurface, along which the solids flow downwardly.

If it is desired to partly or completely prevent the solids that flowdown along the wall cooling surface from being influenced by the risingflue-gas flow, a number of downwardly extending recirculation lines orpassages are provided on the wall cooling surface and are closed orpartly or completely open toward the reactor interior. The chosenconstruction depends on the permitted or desired extent of influence. Asbefore, preferably the walls of the recirculation passages are cooled.

Starting from the device known from WO 83/03294, comprising a labyrinthseparator made up of staggered substantially U-section beams, with thebeams opening toward the flow of flue gas, according to an advantageousfeature, a substantially U-section guide chute for solids is formed onat least one free arm of the separating beams and opens in the directionof the flow of flue gas, i.e. the opening faces away from the oncomingrising flow of flue gas.

In order to improve the conveying action of the separating beams,according to the invention a substantially U-section guide chute forsolids is formed on at least one free arm of the separating beams andopens in the direction of the flow of flue gas.

According to another feature, starting from the known device, theseparating beams have a round cross-section or a cross-section in theform of a polygonal line or course.

Advantageously also, the separating beams comprise pipes that aresupplied with a cooling agent and are disposed in a tube-web-tubeconstruction. The tube-web-tube construction can be studded and bankedfor improved protection against heat and wear. Alternatively, theseparating beam can be made of cast iron.

The separating beams, as in WO 83/03294, can extend substantiallytransversely to the gas flow or at an angle thereto, from one wall tothe other. Alternatively, however, the beams can extend like a roofbetween two opposite wall cooling surfaces.

In order to cool the separating beams and/or the additional boundarysurfaces of the recirculation passages, they can be incorporated in thewater-steam circuit of a boiler, if the device is operated as a boiler.

Advantageously, the recirculation passages are formed from the wallcooling surface and a recirculation line cooling surface at a distancetherefrom and metal plates that extend vertically or perpendicularlybetween the two cooling surfaces; advantageously, the pipe spacing ofthe wall cooling surface is smaller than for the recirculation-linecooling surface, since the pipe on the recirculation-line coolingsurface is used mainly only to cool the walls, with most of the heatbeing dissipated via the wall heating surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will now be described in detailwith reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic longitudinal section through a fluidized bedreactor along line I--I in FIG. 2;

FIG. 2 is a horizontal section along line II--II in FIG. 1;

FIG. 3 is a partial longitudinal section through the fluidized bedreactor of FIG. 1, looking in the direction of the arrows III--III;

FIG. 4 is a longitudinal section through the reactor of FIG. 1, lookingin the direction of the arrows IV--IV;

FIGS. 5 and 6 are cross-sections through preferred embodiments ofseparator beams; and

FIG. 7 is a longitudinal section comparable to FIG. 1, but without anyseparate recirculation lines on the inside of the wall cooling surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As FIGS. 1 to 4 show, a fluidized bed reactor 1 of rectangularcross-section has four wall cooling surfaces 1a-1d of tube-web-tube ortube-fin-tube construction.

In the bottom portion UB of the fluidized bed reactor, fuel 2 issupplied above a valve tray 4 that is supplied with fluidizing gas 3,and a stepped supply of secondary air 5a and 5b occurs above the fuelsupply 2. As shown in FIG. 4, the cross-section widens from the valvetray 4 to the secondary air supply 5a.

In the top portion OB, a labyrinth separator 6 is disposed in two offsetlayers 6a and 6b of separator beams 7. As FIG. 1 shows, the beams 7extend obliquely downwards to the wall 1b, which has connected to thebeams 7. The beams are permanently connected to the walls.

As FIGS. 3 and 4 show, the wall 1d does not extend up to the top 1e ofthe reactor but has an outward bend 1dd that leaves free a gas passage 8into a descending flue 9 connected behind or downstream of thereactor 1. An additional labyrinth separator 10 disposed in thetransition area between the reactor 1 and the flue 9 comprises twolayers 10a and 10b of separator beams 7. The beams extend substantiallyvertically.

As FIG. 2 shows, the flue 9 is bounded by the wall cooling surface 1dand further wall cooling surfaces 9a-9c. At least one contact heatingsurface 11, e.g. a superheater, is disposed in the flue. A dustseparator is disposed in front or downstream of the flue.

As FIGS. 1, 2 and 3 show, a recirculating-line cooling surface 12 oftube-web-tube construction extends at a distance from the wall coolingsurface 1d and has a larger spacing than does the surface 1d. The pipes13 in the recirculating-line cooling surface 12 are connected to pipes14 in the wall cooling surface 1d. Metal sheets 15 extending between thecooling surfaces 1d and 12 define individual recirculation lines orpassages 16.

The passages 16 are open at the bottom end, and the wall 12, in the areaof the bent portion 1dd of the wall surface 1d, extends upwardly to suchan extent that it carries the ends of the beams 7 of the separator 6 andalso allows the gas to flow out at 17 from the reactor into thetransition region and consequently to the gas outlet 8. A collecting anddistribution funnel 18 is also formed between the wall 12 and theportion 1dd; the recirculation passages 16 convey the separated solidmaterial from the funnel 18 to the bottom region UB near the secondaryair supply 5a or 5b.

In a comparable manner, the wall cooling surface 1b is associated with arecirculating-line cooling surface 19 that cooperates with the outwardlybent area 1bb to define a collecting and distribution funnel 20, andalso defines recirculation lines or passages 21 via the interposition ofmetal sheets 15.

Those surfaces of the passages 16 and 21 that face the interior of thereactor can be closed 16a, 21a, or can be formed with apertures 16b, 21bor with continuous longitudinal slots 16c; alternatively, they can becompletely open, leaving only webs at the side. These possibilities arediagrammatically shown in FIGS. 1 and 3; of course, hybrid embodimentson a reactor wall are also possible.

As FIGS. 4, 5 and 6 show, the beams 7 are also of tube 7a--web 7b--tube7a construction. The wall-cooling surface of the reactor 1 and the flue9, the separator 7, and the recirculating-line cooling surfaces 12 and19 are incorporated in a water-steam circuit as diagrammatically shownin FIG. 1, which shows a drum 22 and the corresponding pipe systems. Thelines leading to the drum thus extend through the openings 17 and 8 andthrough the widened region in the top left part of the reactor 1 ofFIG. 1. The number of lines can be equal to the number of pipes, of canbe less if some pipes are combined. The line portions where there is atransverse flow can be additionally protected.

As FIGS. 4, 5 and 6 also show, the beam separators 7 have asubstantially U-shaped cross-section and open towards the flue-gas flowRG. A U-shaped chute 23 for guiding solids is disposed at at least onefree or projecting arm of the U and opens in the direction of theflue-gas flow; thus facilitating the removal of the solids trapped bythe beam 7 into the funnels 18 or 20.

In the embodiment of FIG. 1 the separated solids are protected by thepassages 16 and 21 when recirculated or returned, whereas these passagesare omitted in the embodiment in FIG. 7. Instead, the separated solidsflow down freely along the walls. Alternatively, the recirculatingpassages can also be omitted from the embodiment of FIG. 1.

The first separator 6 also has roof-shaped separating beams 7' andtherefore conveys solid material to two opposite walls 1b, 1d instead ofjust one wall.

Of course, even when recirculating passages are used, the firstseparator 6 can be designed in such a way that it supplies solids to twooppositely-disposed walls.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

We claim:
 1. In an apparatus for burning carbonaceous material in afluidized bed reactor that includes: a bottom portion; a top portion;wall cooling surfaces; a recirculation system that includes at least onelabyrinth separator which serves for the return of separated-off solidmaterial to said bottom portion and is provided with staggered beamsthat have an essentially U-shaped cross-sectional configuration and areopen downwardly toward a rising flow of flue gas; and a fuel supply, afluidizing air supply, and a secondary air supply in said bottomportion; the improvement wherein:said staggered beams are disposeddirectly in said top portion of said fluidized bed reactor in a risingflow of flue gas, are inclined, and guide said separated-off solidmaterial to at least one of said wall cooling surfaces, which define arector interior and along which said solid material flows downwardly;and said separator beams have free arms, on at least one of which isformed a guide chute that has an essentially U-shaped cross-sectionalconfiguration and serves for the guidance of solid material, with saidguide chute opening upwardly in a direction facing away from said risingflow of flue gas, and serving for the removal of solid materialcollected by associated separator beams.
 2. An apparatus according toclaim 1, in which said at least one wall cooling surface is exposed. 3.An apparatus according to claim 1, in which a plurality of recirculationpassages are provided on said at least one wall cooling surface, withsaid recirculation passages extending downwardly from said top portionto said bottom portion.
 4. An apparatus according to claim 3, in whichsaid recirculating passages are closed toward the interior of saidreactor.
 5. An apparatus according to claim 3, in which saidrecirculating passages are partially open toward the interior of saidreactor.
 6. An apparatus according to claim 3, in which saidrecirculating passages are completely open toward the interior of saidreactor.
 7. An apparatus according to claim 3, in which saidrecirculation passages are defined by further wall cooling surfaces. 8.An apparatus according to claim 3, in which a lower region of saidrecirculation passages opens out in an effective range of said secondaryair supply.
 9. An apparatus according to claim 3, in which saidseparator beams have a round cross-sectional configuration.
 10. Anapparatus according to claim 3, in which said separator beams have apolygonal cross-sectional configuration.
 11. An apparatus according toclaim 3, which includes means for cooling said separator beams.
 12. Anapparatus according to claim 11, in which said separator beams comprisetubes disposed in a tube-web-tube construction, with said tubes beingsupplied with coolant.
 13. An apparatus according to claim 3, in whichat least one of said separator beams and said wall cooling surfaces ofsaid recirculation passages are included in a water/steam circuit of asteam generator.
 14. An apparatus according to claim 3, in which saidrecirculation passages are formed by a wall cooling surface, arecirculating-passage cooling surface that is spaced from said wallcooling surface, and by sheets disposed perpendicularly between saidwall cooling surface and said recirculating-passage cooling surface.